Hydrogenation acetophenone

These differences in the performance of Pt/Si02 and tin-modified catalysts agree with previously published information about how the modification of a platinum surface causes a decrease in the hydrogenation rate of acetophenone [114]. 

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A three-step process involving the oxidation of acetophenone, hydrogenation of the ketone to a-phenylethanol, and dehydration of the alcohol to styrene was practiced commercially by Union Carbide (59) until the early 1960s. Other technologies considered during the infancy of the styrene industry include side-chain chlorination of ethylbenzene followed by dehydrochlotination or followed by hydrolysis and dehydration. 

Asymmetric C=0 hydrogenations in water were also reported by Lemaire et al. This catalytic system is based on Ir(cod)L complexes, where L is a hydrophilic chiral C2-symmetric diamine ligand such as p-substituted (IR 2R)-(-i-)-l,2-diphenylethylenediamine derivatives (29a-e Scheme 4.12). The use of such ligands allowed catalyst recovery without loss of activity and enantioselectivity in at least four acetophenone hydrogenation cycles [29]. The ee-values observed in the reduction of phenyl glyoxylate in the water phase were, however, lower than were found when running the tests in THF (Table 4.3), when the substituents were H and Me, and about the same with OH, OMe and 0-(C2H40)3Me. 

Figure 6.14 Product distribution (mol.%) during acetophenone hydrogenation (353 K, 1 MPa H2, 0.25g catalyst) (a) Pt/Si02 catalyst (b) PtSn-BM catalyst (c) PtSn-OM catalyst [(A) AP, ( ) PE, ( ) CHMK, (O) CHE and ( ) EB and ECH] see text for details (Reproduced from Reference [34].)...

The practical application of a catalyst not only depends on its catalytic activity but also on its stability. Therefore, it was of interest to study the stability of the three catalysts during three successive acetophenone hydrogenation reactions. Tests carried out for this purpose consisted in hydrogenating acetophenone until reaching 100% conversion. The catalyst was then washed with isopropyl alcohol and allowed to act again, so that catalysts were tested in a series of three hydrogenation cycles. 

Acetophenone Hydrogen chloride Magnesium 5-Chloro-2-norbomene Piperidine hydrochloride Formaldehyde ... 

Furthermore, Avecia has developed the Rh-cyclopentadienyl complexes in Fig. 3.36 for the large scale production of 1-tetralol and substituted 1-phenyl-ethanol [102]. The challenge in this area is to increase the activity of the catalyst. Recently, Anders son and co-workers reported an azanorbornane-based ligand which can reach a TOF up to 3680 h-1 for acetophenone hydrogenation (see... 

The possible reaction scheme of acetophenone hydrogenation on a metallic catalyst could be described as follows ... 

The overall reaction path for acetophenone hydrogenation is represented in Scheme 1. On pure silica supported rhodium, the total conversion of acetophenone is achieved in less than... 

Figure 3.4. Initial rate of rate of acetophenone hydrogenation (without solvent) as a function of the relative amount of the aqueous phase. Catalyst [RhCt(PPh3)3]. [Rh]= 0.002 M, [EtjN]/[Rh]= 2, 50 °C, 1 bar total pressure. Reproduced with permission from J. Organometal. Chem. 1982, 231, 63. Copyright (1982) Elsevier Sequoia S. A.

The increased activity over Ni/Ti02 is probably due to the creation of highly active sites at the metal support interface (7). Further, increase in activity over Ni-Fe/Ti02 is due to synergetic metal support interaction and electronic effect of Fe as reported earlier for acetophenone hydrogenation (2). 

The selectivity to benzhydrol is dependent on the solvent and can be correlated with the dielectric constant of the solvent similar to earlier findings of Masson et al. (14) for acetophenone hydrogenation. Addition of NaOH results in an increase in the selectivity at the expense of drop in activity. However, this can be partly compensated by using methanohwater as a solvent. Using this combination it was possible to achieve high selectivity to benzhydrol (98.4% selectivity at 88% conversion) at reasonable activity. 

Scheme 18.14 Role of adatoms in the selectivity of acetophenone hydrogenation (on Rh and RhSnoj).

Figure 10.4. Effect of EtaN on enantioselectivity of acetophenone hydrogenation with a [Rh(NBD)Cl]2 + (-)-DIOP catalyst.

Drelinkiewicza, A., A. Waksmundzka, W. Makowski, J.W. Sobczak, A. Krol, and A. Zieba. 2004. Acetophenone hydrogenation on polymer-palladium catalysts. The effect of polymer matrix. Catal Lett 94 (3-4) 143-156. 

Hasanayn, P. Morris, R. H. Symmetry aspects of H2 splitting by five-coordinate d6 ruthenium amides, and calculations on acetophenone hydrogenation, ruthenium alkoxide formation, and subsequent hydrogenolysis in a model trans-Ru(]4)2(diamine)(diphosphine) system. Inorg. Chem. 2012,51,10808-10818. 

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